Inaccuracy in Airguns

Inaccuracy - What Causes It?

Occasionally our phone conversations concern a customer's airgun which "can't hit the broad side of a "barn." Invariably, the frustrated owner has "tried everything, but the gun still won't group well no matter what!" Unfortunately, the information supplied with most new airguns is fairly sparse at best and don't offer much assistance, so here is a list of the frequent problem areas to look at before you give up in despair.

Most of this information applies to conventional spring piston airguns but is appropriate to other systems as well.

Loose Stock Screws are probably the most common cause of inaccuracy in airguns. Even a quarter turn loose can translate to 50mm difference at 25 meters. Most airguns have screws securing the action to the stock (two in the forearm, one through the front of the trigger guard and one in the rear of the trigger guard). These must be firm at all times.
Loose screws on the breech-block assembly will also affect accuracy on break-barrel models. CAUTION! Before you stampede to your tool box - airgun screws, just like regular firearm slotted screws, are different. They require special screwdrivers with parallel tapers unlike carpentry screws. Use a regular screwdriver and you risk damaging the screw head and the gun.

Loose Sights. On Open Sight guns - check that the front sight attachment screw is tight and the sight element held within is secure. Check the rear sight for play and tightness on the breech block.

Scope Mounts - Any old scope mount just won't do on an airgun! On magnum, super-magnum springers and PCP's, you must use a scope mount specifically designed for airgun use. Many airgun mounts have a "stop pin" that fits in special holes at the back of the receiver and their bases range in width from 11mm-14mm depending on the brand. These stop pins are necessary because spring piston airguns don't just recoil backwards, they snap forward too. And when coupled with the vibration of the mainspring can drive an improper mount off the scope grooves. Separate scope stops are also available for the same purpose. Scopes can also move through the scope rings (scope creep) but this problem is usually eliminated by using the right scope mount.

Using a Regular Firearm Scope. Leave your old .22 scope on your .22 rimfire! If you are serious about your airgunning and want the best performance out of your airgun, you must use a scope specifically designed for airgun use. American firearm mounts, for example, will not fit properly because they are either 3/8" or Weaver (3/4") in width. Don't get conned or laughed off at your local gun shop! Today's magnum spring piston and gas spring airguns will promptly break a less than proper airgun scope.

As mentioned previously, airguns recoil backwards then snap forward. This action is what destroys regular, non-airgun scopes. Proper airgun scopes have their lenses and reticles braced at the front and the back whereas most regular firearm optics are only braced at the rear. This double recoil peculiar to airguns, coupled with the vibration of the mainspring, will quickly destroy even the biggest brand names in scopes. But be aware that even airgun scopes can be rated for Light, Medium and High Recoil rifles. We, at Straight Shooters rate all our scopes for the proper use so it's easy to match a scope to the power of the gun you choose.

Secondly, airguns shoot at shorter distances than regular firearms and most regular firearm scopes are parallax corrected for 100 yards or more. Proper airgun scopes have an externally adjustable parallax ring on the front end objective or a side focus knob to focus clearly at all distances down to about 10 yards or 10 meters. This can also be used as a range finder to estimate distances to your target.

Finally, airguns have a much more pronounced trajectory than firearms and airgun scopes have an elevation bias so there is more up than down adjustment, eliminating the need to shim the scope mount and possibly crush or bend the scope tube.

Incorrect Barrel Tension. Barrel cocking airguns must have the pivot tension set carefully. Too much and the barrel detent will not consistently lock up and there will be galling of the breech block. Too little and there will be blow-by at the breech. Both situations will cause erratic groups. The correct tension is the point where the barrel will just stay anywhere on the return arc after cocking. Better barrel cocking airguns have adjustable pivot tension. You must use proper gunsmith screwdrivers, keep your fingers out of the trigger guard and don't adjust a cocked gun!

On Beeman R series and Weihrauch rifles, loosen the right hand side screw/nut and tighten the left hand side bolt. When the tension is correct, tighten the nut against the bolt and recheck. On Diana, Anschutz and others, remove the small lock screw and tighten the pivot bolt to a compromise position that allows the lock screw to locate into one of the cutouts in the pivot bolt head.

The Wrong Pellet. Most inaccuracy queries emanate from owners of .177 magnum sporters capable of muzzle velocities in excess of 1000 fps. In the power race, many manufacturers use the very lightest pellet available to achieve their advertised velocity and boost their sales. Invariably, this pellet is not the best for these guns, in terms of accuracy, energy and velocity retention downrange where it counts. Every gun barrel is slightly different and the pellet that groups best in one gun may not work with the next gun even if it is the same make and model. Powerful spring guns work better with medium heavy or heavy pellets rather than light pellets. This will decrease the velocity but increase the accuracy. Buy an Straight Shooters Pellet Sampler in your caliber, and see which pellets shoot the best group at your preferred shooting distance.

Pellet induced accuracy problems on lower powered airguns can usually be cured by switching brands or types. Don't use old and oxidized pellets or any deformed examples, but rather discard them immediately. Only use high quality lead pellets from respected manufacturers. Cheap pellets are false economy.

Dirty Bore. Airguns do foul barrels but not in the same manner as regular firearms. Instead, minute traces of lead and the gun's mechanisms spray lubricants from the compression chamber leave deposits in the rifling. This must be carefully removed with a proper airgun barrel cleaning kit. We strongly recommend the Napier cleaning kit . These kits use a compact flexible rod that won't damage the delicate crown or rifling and cover all four calibers. Carefully follow the directions for the best results. Don't use regular firearm solvents because they will attack the seals. Use a gentle degreaser such as Napier Airgun Oil on a pure cotton patch and make sure the bore is dry before applying a very light coat of polarizing oil to protect against rust. A good quick fix in the field is to use ." If you don't care for flexible cleaning rods, you can also use a rigid rod such as a J.D. Dewey rod, some cleaning patches and Napier Airgun Oil to do the job.

Reviews

I recently purchased a Theoben MFR in .20. It was tuned to run on the Beeman Kodiak heavies. Knowing that these were those I bought four tins. Should have bought 8! Exceptional shooting pellet. They were also great shooters out of another .20 cal rifle I have. A custom Lothar walther barreled Crosman. So far only shot out to 50 yards. Went through a full tin in only three days of shooting.